The current telecommunication service providers' networks reflect the architecture of the PSTN network as it has evolved over the last 100 years. This is largely based on circuit switched technologies. Initially, all telecommunication services were offered via a wired infrastructure. As the user-base increased and requirements changed over the last few decades, new types of services were created e.g. wireless PSTN, cable video, multi-service (PSTN, video, satellite). The networks that supported these services were created as parallel networks, along-side the existing PSTN network. As technologies matured, there was some convergence (e.g. they shared the same SONET backbone) in the network architecture. During the late 1980s, with the explosion of data networking and Internet, data networking networks like frame relay and ATM were developed, and later large internet based data networks were constructed in parallel with the existing PSTN infrastructure. These data networks again shared the PSTN infrastructure only at the SONET backbone layer. This state of current networks is called the existing "Core". Thus the "Core" network is a set of parallel networks; PSTN, wireless, satellite, cable, ATM, frame relay, IP. There is some interoperability between the services on these parallel network (e.g. PSTN, and wireless), but generally these networks are vertically integrated to provide distinct set of non-interoperable services.